How NOT to Tap a Hole

[Janderso]

An extreme version, but one I've seen over and over in modern industry. It's what happens when you let college educated bean counters (accountants) run things. Glad I'm out of even the independent contractor business.

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Too many officers, not enough NCO's

 

[Suzuki4evr]

And that is how MrWhoopee bacame MrWhoopsee . It happens to all of us.

 

[hman]

An extreme version, but one I've seen over and over in modern industry. It's what happens when you let college educated bean counters (accountants) run things. Glad I'm out of even the independent contractor business.

Please, Bill! Calling them "bean counters" is considered impolite nowadays. They're "Enumerators of Legumes"

 

[Bi11Hudson]

Too many officers, not enough NCO's

Too many chiefs, not enough Indians. (?Politically Incorrect?)

Please, Bill! Calling them "bean counters" is considered impolite nowadays. They're "Enumerators of Legumes"

My father was a "Book Keeper" in the days before it required a college degree. He referred to the college graduates that worked under him as "Bean Counters". I just repeat what I was taught. And I am often intentionally impolite, just to stir the $h!^ can.

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[zuhnc]

A company I used to work for, in the 90's purchased a bankrupt company that was in the same field of business. One of the first things the new "Legume Counters" and "Big Dogs" did, was scrap ALL the current inventory and documentation. Now, all the field technicians had NOTHING to work with when repairing that equipment in the field. I suppose the thinking was, "If we make sure there are no parts or documentation available, then our customers will have to buy new equipment". A lot of the customers did just that, but bought their new equipment from competitors, at a less expensive price.

 

[C-Bag]

"If we make sure there are no parts or documentation available, then our customers will have to buy new equipment". A lot of the customers did just that, but bought their new equipment from competitors, at a less expensive price.

I love it when the "market" has the option of going somewhere else and giving the one finger salute to those greedy maroons.

The last co I worked for was bought out by an overseas co and was using the old American co's name to insinuate themselves into the American market. If the two designs, US and foreign were set side by side, the folks here would always buy the US design. It was heavier duty, nicer finish and just looked solid. So they started modding the foreign design making it more robust and getting rid of the stuff anybody who had any clue about machinery would reject. They were expanding and could hardly keep up.

Meanwhile it wasn't going the way the mother co thought it would go because nobody would buy the foreign design. And they were wanting no other option but to buy their junk. Right as they were getting rid of the last of the domestic hierarchy and installing the son of the foreign owner as CEO, I bailed. Last I saw they had quit expanding and were trying to get back the market they'd had.

 

[Dan Krager]

I learned the hard way that QC in my little hobby shop is still important. In making a set of large hand screws for my woodworking interests, I cut some 1/2" rod for the 1 1/2" long swivel pins and threaded a mid-pin cross hole in each, half LH and the other half RH 3/8-16. I held the pins in a 1/2" 5c collet in a square block mounted in my vise. Drilled and tapped about 4 dozen and when assembling the clamps (after struggling with 9" of LH and 7 1/2" of RH threads on an 18" rod) found out that the threaded pin holes were not at 90° to the pin. They were off varying amounts up to 10°. How could that happen:? I puzzled over that for a long time until I realized that probably the unsupported end of the pin sagged under drilling pressure. Reading up about how collets hold work, I learned that only the ER collets (split on both ends) can adjust their grip to fit the rod. All the others like R8 and 5C force the end closed leaving the work "loose" inside the collet. So my pins sagged and I didn't notice. The problem could have been solved with a machinist jack had I checked for quality. So the replacements will be held against a stop in a grooved jaw of a freshly fettled machinist vice.

zu früh alt, zu spät klug
DanK

 

[RJSakowski]

I learned the hard way that QC in my little hobby shop is still important. In making a set of large hand screws for my woodworking interests, I cut some 1/2" rod for the 1 1/2" long swivel pins and threaded a mid-pin cross hole in each, half LH and the other half RH 3/8-16. I held the pins in a 1/2" 5c collet in a square block mounted in my vise. Drilled and tapped about 4 dozen and when assembling the clamps (after struggling with 9" of LH and 7 1/2" of RH threads on an 18" rod) found out that the threaded pin holes were not at 90° to the pin. They were off varying amounts up to 10°. How could that happen:? I puzzled over that for a long time until I realized that probably the unsupported end of the pin sagged under drilling pressure. Reading up about how collets hold work, I learned that only the ER collets (split on both ends) can adjust their grip to fit the rod. All the others like R8 and 5C force the end closed leaving the work "loose" inside the collet. So my pins sagged and I didn't notice. The problem could have been solved with a machinist jack had I checked for quality. So the replacements will be held against a stop in a grooved jaw of a freshly fettled machinist vice.

zu früh alt, zu spät klug
DanK

Collets like the R8 a 5C will grip along their full length providing: 1. The difference between nominal and actual diameter isn't too great and 2: the force used to close the collet is sufficient. As no. 1 increases, no. 2 has to increase as well.

If you look at the collet geometry, there is an angle between the taper and the cylindrical inner bore. The tool or part being held is cylindrical and the taper of the socket matches the collet. In order for the full length fit, the spring portion of the collet has to distort into an "s" curve which takes more force than a simple arc. A greater difference in diameters requires considerably more force which is why manufacturers of collets like the 5C recommend limiting the grip range.

Actually, An R8 or 5C collet will grip properly as long as the slits on the face of the collet haven't completely closed. The difference between the nominal and actual diameters is 15% greater than the slit width. slit widths on my 5C and R8 collets varies between .007" for my smallest collet to .06" for the larger collets.

One must realize that whenever there is a difference in diameters, the actual contact area is three lines 120º apart much like a drill chuck. That is the reason for using a machinable collet where the collet diameter is bored to match the part diameter. For most purposes, though, the three line contact is sufficient for accurate machining, providing the collet is closed sufficiently.

 

[addertooth]

These problems are not limited to the Machining and Fabrication world. In the electronics/instrumentation/computer/networking industries... the same kind of stories are observed. Test Engineering instrumentation companies regularly buy out each other. The old crew is sent away, and a new crew (which has no familiarity with the product) is brought in. Contracts for custom chips (used to make the instruments), are allowed to laps, and availability of replacement parts go away. If you think it is tough to fabricate a replacement part for a mill, imagine having to Design your own integrated circuit chip for a main board. A long trail of orphaned products litter the landscape. This kind of action can turn a million dollar piece of test equipment into a paperweight.